4.9.1 Using getline with No Arguments

The getline command can be used without arguments to read input
from the current input file. All it does in this case is read the next
input record and split it up into fields. This is useful if you’ve
finished processing the current record, but want to do some special
processing on the next record right now. For example:

This awk program deletes C-style comments (‘/* …
*/’) from the input. By replacing the ‘print $0’ with other
statements, you could perform more complicated processing on the
decommented input, such as searching for matches of a regular
expression. (This program has a subtle problem—it does not work if one
comment ends and another begins on the same line.)

This form of the getline command sets NF,
NR, FNR, RT, and the value of $0.

NOTE: The new value of $0 is used to test
the patterns of any subsequent rules. The original value
of $0 that triggered the rule that executed getline
is lost.
By contrast, the next statement reads a new record
but immediately begins processing it normally, starting with the first
rule in the program. See Next Statement.